1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier or printer provided with a function to form images on a recording material such as sheets.
2. Description of the Related Art
From the viewpoint of media flexibility, the following method is available to an electrophotographic color image forming apparatus. The method involves, after forming toner images on a photosensitive body, transferring (hereinafter, primary transfer) the toner images to an intermediate transfer member (intermediate transfer belt), forming the toner images of multiple colors one on top of another on the intermediate transfer member, and then transferring (hereinafter, secondary transfer) the toner images to a recording material. This method requires cleaning of the intermediate transfer member because part of the toner is left on the intermediate transfer member without being transferred to the recording material after the secondary transfer.
Available cleaning methods include a method which removes toner left on the intermediate transfer member using a blade, fur brush, or the like, and collects and contains the toner in a residual toner container. However, this method requires a transport unit for transporting the toner to the residual toner container. Also, the method requires a user to replace the residual toner container, and thus is not desirable from the viewpoint of usability.
To solve this problem, the following cleaning methods have been proposed and put to practical use.
Japanese Patent Application Laid-Open No. H09-50167 discloses a charging member adapted to charge remaining toner on the intermediate transfer member to a polarity opposite to the original charge polarity of the toner. In a transfer portion of a photosensitive drum disposed downstream of the charging member, toner images are transferred from the side of a photosensitive body to the intermediate transfer member by normal image formation and the oppositely charged toner remaining on the intermediate transfer member after secondary transfer are electrostatically attracted and moved to the photosensitive body to replace the toner images. The toner remaining after the secondary transfer and transferred to the photosensitive body is collected by a cleaning portion on the photosensitive body. Japanese Patent Application Laid-Open No. 2005-227308 discloses a configuration for downsizing an apparatus by using a common counter member for a charging member and secondary transfer member.
There is the following problem in a configuration in which multiple image bearing members are placed below the intermediate transfer belt in order to reduce the interval between the time when electrostatic latent images start to be formed by exposure of the multiple image bearing members with an exposure unit and the time when toner images are secondarily transferred to a transfer material. Among configurations in which multiple image bearing members are placed below the intermediate transfer belt, a configuration in which the exposure unit is placed below the multiple image bearing members is known generally.
Suppose a counter member is shared by the charging member adapted to charge residual toner and the secondary transfer member as described in Japanese Patent Application Laid-Open No. 2005-227308. Then, depending on the situation, the remaining toner charged by the charging member subsequently moves a long distance by being carried by the intermediate transfer belt until coming into contact with the image bearing members. If the charge of the residual toner on the intermediate transfer belt decays during the movement, the residual toner will scatter from a bend of the intermediate transfer belt or will have difficulty in moving to the image bearing members in a primary transfer portion.